This invention relates to fibres, yarns or threads which include radio opaque material.
Radio opaque multifilament yarns are included in surgical swabs so that they can be identified by X-rays. Such yarns must contain at least 55% by weight of radio opaque material in order to meet the specification of the British Pharmacopoeia. In the past, radio opaque yarns have been produced from viscose loaded with up to 60% barium sulphate. However these yarns possessed several shortcomings. The viscose component was affected by wet processing of the yarn during incorporation into woven gauze. Length changes occurred and excessive tensions were apparent. The viscose component was subject to brittle fracture at low stress leading to fragmentation. The nature of the wet spinning process made it very difficult to maintain product consistency.
Polypropylene has been assessed as an alternative carrying medium to viscose. Polypropylene being hydrophobic is not subject to dimensional changes caused by wet processing. Barium loaded polypropylene yarns have been made. However at loadings in excess of 45% by weight extensive loss of strength has been observed in multifilament yarns. Extrusion of filaments at loadings in excess of 45% has been difficult due to barium sulphate agglomeration. Twisting the low strength filaments also poses many difficulties.